A four-and-a-half-year jail sentence handed to a thug who killed a man with a single punch in an unprovoked attack could be referred to the Court of Appeal.

Andrew Young, 40, died after being struck by Lewis Gill, 20, in Bournemouth, Dorset, on November 6 last year, in a vicious assault caught on CCTV.

Gill later pleaded guilty to manslaughter and was sentenced at Salisbury Crown Court to four-and-a-half years in prison - a sentence reportedly branded an "absolute joke" by Mr Young's family.

The Attorney General's Office has confirmed it is considering whether to refer the sentence to the Court of Appeal for being unduly lenient after receiving complaints. Only one complaint is required to trigger the process.

The Attorney General has until March 21 to decide whether to refer the sentence to the Court of Appeal.

CCTV images of the assault show Asperger's sufferer Mr Young challenging a cyclist who was riding his bike on the pavement.

After one minute of discussion between the pair, Gill - an acquaintance of the cyclist - arrives at the scene.

The cyclist rides off and Gill appears to turn to follow him - but suddenly lunges towards Mr Young and launches a single vicious punch at his head.

Mr Young immediately falls on to the ground, where he lies motionless.

Gill, of Sutton in south London, glances back at him before callously walking away.

Dorset Police released the CCTV images, which were shown to the sentencing judge.

Detective Inspector Marcus Hester, of Dorset Police's major crime team, said: " This was a violent attack on an innocent man, which had a tragic outcome.

''This case shows that violence does not resolve anything and can have far-reaching consequences not imagined at the time.

''Today the court has issued a sentence deemed appropriate and in accordance with the evidence put to them.

''Criminal behaviour such as this will not be tolerated and we are committed to bringing offenders to justice.''

The incident happened on November 6 last year outside the Tesco Metro store in Charminster Road, Bournemouth.

Mr Young suffered a serious head injury and later died in Southampton Hospital.

Gill is to serve a further six months' imprisonment for other matters.

Victims' Commissioner Baroness Newlove, whose husband Garry was killed by a gang vandalising his car, said: " I'm appalled by this disgraceful act of violence - my thoughts go out to the victim's family and friends at this time.

"It's entirely right that the sentence will be reviewed for this shocking crime.

"I know how traumatic it is to go through the courts as a victim - when you are already so hurt and vulnerable. That's why I urge everyone involved in this case to put victims first in the pursuit of justice."